No one needs a definition of a mass shooting anymore; they have become too common. But there is growing evidence that mass shootings may act like a contagion, because some perpetrators appear to have studied past mass shootings in an effort to emulate them.
Researchers who study violent behavior say that many, if not most, perpetrators of these crimes have studied earlier mass shootings and have expressed an admiration for the people who commit these crimes. The publicity that surrounds any large-scale crime may be causing other mentally ill and angry would-be killers to speed up their path to violence.
The man who killed nine people at a community college in Oregon reportedly watched videos of the 2012 massacre at an elementary school in Connecticut. In turn, that man had studied the shootings at a Columbine High School in Colorado in 1999 and a massacre in Norway in 2011 where 77 people were killed. But experts emphasize that many factors, including mental health issues, may motivate a mass killer.
Mass shootings may be a type of cultural contagion, and as with contagious diseases, it may require a public health response. Such a response should focus on both early detection and preventive measures as well as on gun control measures.
Some people have also suggested that there should be changes in the way the news media covers mass killings.
"If you blast the names and faces of shooters on news stations and constantly repeat their names, there may be an inadvertent process of creating a blueprint," said Dr. Deborah Weisbrot, an associate clinical professor of psychiatry at Stony Brook University in New York, in an interview in The New York Times.
At least one study suggests that mass killings, like teenage suicides, may "cluster," with one highly covered case quickly followed by others. In a recent analysis of hundreds of killings from 1997 to 2013, researchers found that the probability of another attack was highest in the two weeks after a killing hit the news.